Harnessing Solar energy, Options for India

1. Introduction
Solar Thermal Applications
Solar thermal technology harnesses solar energy into thermal energy for non-electrical applications,
and is already a mature and economically viable option. The solar thermal collector capacity in
operation worldwide equalled 151.7 GW th, corresponding to 217 million m 2 , by the end of the year
2008, with the main markets in China (87.5 GW th) and Europe (28.5 GW th). 1 The majority of the solar
thermal technologies operating today provide hot water to households for both sanitary purposes
and space heating. 2
While solar water heating is well established, it is crucial that the potential of solar thermal
technology in other applications in the residential and industrial sectors are analysed as well. In the
residential sector, solar cooking has the potential to reduce the use of traditional firewood and
biomass. In the industrial sector, process heat is used in multiple industries, such as, food (for
cleaning, drying and pasteurisation), machinery and textile (for cleaning and drying). Approximately
30% of the heat energy used in industry is below 100°C and 57% is below 400°C. 3,4 Working
temperatures for some of the thermal applications are shown in Figure 18. Given the demand for
heat at low to medium temperatures, the potential use of solar energy is enormous. It is estimated
that solar energy could provide 3.8% of the total energy consumed by industry in the European
Union (EU 25). 5
Industrial
Process Heat
Application
Solar Water
Heater
Solar Drying
Solar Cooking
0 100 200 300 400 500
Temperature (Degree Celsius)
Figure 18: Thermal Applications and Working Temperatures
(Source: CSTEP)
For low temperature applications of up to 100°C, such as for solar drying, water heating and
industrial heat processing, flat plate collectors (FPC) and evacuated tube collectors (ETC) are
prevalent. An FPC is the most common type of non-concentrating solar collector. It consists of a dark
flat plate that absorbs the solar energy and is backed by an insulated fluid tube with a glass or
polycarbonate cover. ETCs have multiple glass tubes that heat up solar absorbers, which ultimately
heat the solar working fluid. For high temperature applications (greater than 100°C), for example,
cooking and process heat, concentrated solar thermal technologies such as the parabolic trough can
be used.
Solar Thermal Applications CSTEP | Page 91